Def == {i:| 0i }

Thm* Type

Def nth_tl(n;as) == if n0 as else nth_tl(n-1;tl(as)) fi (recursive)

Thm* A:Type, as:A*, i:. nth_tl(i;as) A*

Def tl(l) == Case of l; nil nil ; h.t t

Thm* A:Type, l:A*. tl(l) A*

Def AB == B < A

Thm* i,j:. ij Prop

Def ij == j < i

Thm* i,j:. ij

Def A == A False

Thm* A:Prop. (A) Prop

Def i < j == if i < j true ; false fi

Thm* i,j:. i < j

Def b == if b false else true fi

Thm* b:. b